Sites have been
selected along two depth transects and one linking latitudinal
transect 12° longitude. The latitudinal transect extends from
near the estimated glacial position of the SAF (51°S) to north
of the modern position of the STC (39°S). Within a single leg of
drilling, a tradeoff is required between providing either (1)
fewer and shorter extremely high-quality (triple advanced
hydraulic piston corer [APC]) records through mainly younger
Neogene sediment; or (2) a greater number of high-quality (double
APC) records that cover a wider geographic range, and some of
which penetrate back to the critical 35-20 Ma interval over which
the South Tasman and Drake Passage gateways opened. We have
approached this tradeoff by scheduling triple-APC coring on the
primary Chatham Rise transect, and double APC at most other
sites.

1. The
Chatham Rise Transect (Sites SWPAC-2B, 5B, 9B)
This transect comprises three holes in water depths between 615 m
and 3308 m located in a northeast band across major sediment
drifts of the Chatham Rise. All sites are above the modern CCD,
recently determined to be at ~4750 m in this area (McCave and
Carter, 1997). Sections span an inferred age of early Miocene to
Holocene, within a thickness of 400-750 m. Two sites (Sites
SWPAC-2B and 4A) terminate in presumed Oligocene sediment, which
marks the regional inception of strong bottom-water flow into the
Pacific.

2.
Campbell Plateau Transect (Sites SWPAC-1C, DSDP 594, SWPAC-6B,
7B)
This transect commences with Site SWPAC-1C in 315 m of water on
the eastern South Island shelf (Canterbury Drifts; to sample
upper AAIW and basal thermocline water), then passes southeast
close to DSDP 594 to link to two sites near the eastern edge of
the Campbell Plateau, Sites SWPAC-6B and 7B. Site SWPAC-6B (543 m
water depth) is targeted to sample AAIW. Biopelagite is present
at the surface and expected to extend downhole to the target
depth. Sedimentation rate in a nearby core (F-121) is <1 cm/k.y., but from the thickening of seismic intervals toward Site SWPAC-6B, significantly higher rates are expected there. Site SWPAC-7B is situated on the crest of the large Campbell Drift, and at 4505 m lies close to the regional CCD. However, monospecific benthic and planktonic isotope records from a site to the north at 4802 m and pilot studies of bulk carbonates (Shackleton et al., 1993) suggest that an isotope record may be determinable with paleomagnetics and perhaps tephrochonology as additional means of age control.

The
Campbell Plateau transect will yield a terrigenous silt record of
late Miocene to Holocene fluctuations in current strength near
the AAIW/thermocline transition (Site SWPAC-1C), a mainly
carbonate record of the Neogene AAIW paleohydrography of the
Campbell Plateau (Site SWPAC 6B), and a mixed carbonate-abyssal
mud record of Neogene paleohydrography of the DWBC (Site
SWPAC-7B).

3.
Linking Latitudinal Transect (Sites SWPAC-7B, 8A, 2B, 9B)
This transect spans a latitudinal range from 51°S to 39°S,
commencing on the Campbell Drift (Site SWPAC-7B, Campbell Plateau
transect) and passing through the North Chatham Drift (Site
SWPAC-2B, Chatham Rise transect). The addition of two other sites
makes up the transect: Site SWPAC-8A near 47°S on the north
levee of the Bounty Fan, and Site SWPAC-9B at 39°S on the Rekohu
Drift.

The
latitudinal transect has been inserted to better track movements
of fronts (STC, SAF, and possibly the AAC) during glacial and
interglacial cycles. Penetration is therefore limited to the
Pliocene-Pleistocene (last 3 m.y.) at Site SWPAC-8A. This site is
also deliberately located on a fan levee to retrieve sedimentary
process information, particularly on the frequency of turbidity
currents and their potential as a proxy for paleoseismic events
and the glacial/interglacial switching of sediment supply into
the DWBC system.

Alternate
Sites
Drilling plans for the alternate sites are discussed in the Site
Summary Section (pages 62 and 65).